Just to get this straight:
One-way and Spool are 2 different things.
One-way is when you are on power, the one-way bearing locks up the diff, thus it acts like a spool, giving power to both wheels at the same time. When off-power/braking, the one-way bearings continue to turn the front wheels independently, so the car only has rear braking. Since this is the case, if you brake too hard, the car may spin-out. The advantage of one-way is that it gives the car a better turn and that it provides minimal wear on the drive line, universal shafts, cups, tires etc. 1-way is for a very smooth driving style racing.
Spool is basically a solid axle, so the front wheel does the same thing as the rear wheels. ie a full-time 4wd, whether its on-power or off-power. but because of that, there is NO diff action on the front wheel. both wheels will rotate at the same rate. so for cornering, it tends to 'push' if the speed is too fast. however, the advantage of it is you can brake very late and very hard into a corner and not worry about spinning out. But because of this, there is more wear-n-tear for the car. spool is for a very aggressive driving style racing.
having said all this, you can actually try out spool for free with the normal gear diff. all you have to do is stuff some tissue paper and jam the gears inside. For 1-way, you will have to buy a 1-way diff to try. As for the tamiya/3 racing 1-way diff, you will need to buy a different set of universal swing shaft to work, since the diff out cups is a lot smaller than the orginal plastic kit out cup.
hope this helps.